The invention relates to a method for modulating the boost converter operating mode of a push-pull converter. The invention particularly relates to a method for modulating the boost converter operating mode of a bidirectional push-pull converter.
Although the present invention and the underlying set of issues are explained with the help of a bidirectional push-pull converter, said invention can also be applied to any other push-pull converters, in which a boost converter operating mode is provided.
Bidirectional DC-DC converters are typically used in situations where electrical energy is to be transmitted in two directions. Said bidirectional DC-DC converters are therefore useful in hybrid electric vehicles for transmitting energy for a high-voltage network to a low-voltage network and vice versa. For example, a 12 volt battery can be charged with the help of a DC-DC converter in the buck converter operating mode, whereas the boost converter operating mode can be used as required for charging or respectively for operating an auxiliary energy storage system for the short-term power requirement (for example during startup) of several hundred volts. Depending on the application, a galvanic separation between the high-voltage and low-voltage side is required for the DC-DC converter so that it is advantageous in some cases to embody the DC-DC converter as a push-pull converter.
The printed publication: Nene H., “Digital Control of a Bidirectional DC-DC Converter for Automotive Applications”, Applied Power Electronics Conference and Exposition (APEC), Long Beach (Calif.), USA, 17-21 Mar. 2013 (doi: 10.1109/APEC.2013.6520476) describes a bidirectional push-pull converter, which is configured on the high-voltage side with a full bridge circuit and on the low-voltage side with a center tap. Furthermore, a current sensor device is provided on the high-voltage side, which is designed to measure the current through the transformer. In the buck converter operating mode, the so-called phase-shifted method is used as the modulation method for actuating the push-pull converter. In the boost converter operating mode, a method is used, in which no current flows in phases on the high-voltage side.
Up until now, an additional current sensor device has been required in the low-voltage circuit for the controlled boost converter operating mode. This makes a complicated configuration of the low-voltage circuit necessary.